Warner Bros’ brief for the title sequence to the remake of Invasion of the Bodysnatchers pushed Prologue Films to get right under the project’s skin - in more ways than one.

Few films have the epic cult status of Don Siegal’s 1956 sci-fi shocker Invasion of the Body Snatchers, a reputation that was enhanced by the 1978 remake starring Donald Sutherland.

Now a second remake has been made - The Invasion, starring Nicole Kidman – and the pressure on the teams behind it not to disappoint filmgoers and critics alike was immense.

No more so than for Prologue Films, which captured the tone of the movie by crafting an absorbing title sequence that is a pathogenetic voyage inside a human body under attack. It’s viral marketing made real.

Prologue creative director Danny Yount says the sequence echoes a portion of the script, which went into the body at a cellular level.

“The director wanted something that looked like scientific animations of cells that were breaking up – as though there was chaos that altered the DNA of someone who is becoming a snatcher,” he says.

It was easier said than done. “I started researching that visual language, and found that most things like that are rendered poorly and look cheap,” reveals Yount. It prompted him to go with something that was more photographic.

“I’ve always been amazed by electron microscopy, and found some great images that I made a storyboard with.”

Yount at first opted to start the cellular journey inside the body and exit through the skin, “as though the process of becoming a ‘snatcher’ had completed its cycle”.

To create these frames he smeared Vaseline all over his arms and face, and took photos of them. Although the concept was well received, it was decided instead to go with the idea of starting the journey in space before entering the body, and then ending in an exterior, lab- like location.

An important step towards creating an authentic look was bringing in experienced medical CG artist and animator Eric Keller. “I had him and another artist called Audri Phillips make a lot of wireframe animations of a terrain,” says Yount, “and asked them to make very slow camera moves that were 10-20 seconds each, which we then edited to some music and put titles over.”

Another key contributor was Maya CG designer and animator DongHo Lee Dong, who had worked on Superman, so knew how to do space scenes very well.

The director liked what Yount was doing, so Prologue went to work texturing, rendering and compositing the scenes. The most taxing part of the process for Prologue was developing a unique look for its stylized depictions of intracellular mechanisms.

“We used a variation of the well-known electro-magnetic scanning look to achieve this, but stayed away from creating a look that audiences have seen a hundred times,” says lead VFX artist Keller.

“Danny specifically requested we avoid the typical ‘fishbowl’ look you see in a lot of scientific animations.”

The biggest technical challenge, says Keller, was making the scenes look great both close up and from a distance, something that required creative use of displacement maps and texturing, so scenes would render in a timely fashion.

“I used the same environment model for several different shots, and created medium- and high- resolution meshes, depending on the shot.”

For crafting the CG cellular environment, Keller says that almost every model started out in Pixologic’s ZBrush 2.0.

“This was the first time I’d used ZBrush for environments as opposed to creating creatures and characters, but it actually worked very well, because ZBrush is ideal for this type of organic modelling.”

Subdivision modelling

Keller adds: “The sculpting interface is quite responsive, and it allows for the creation of extreme detail without much of a performance hit while working.

“The ability to export the same model at a number of different subdivision levels made it much easier when it came to animate in Maya. Models in the distance can be at a lower subdivision level than those close up.”

In addition, he was able to export the finer-detail elements as displacement maps for use in Maya, a technique used frequently for the bacterial organisms in the sequence.

Keller used ZBrush to pose the organisms, which were exported to Maya as .obj models and then used as blendshape targets. He used Maya for rendering and animation, the goal being to create a random, organic movement to some of the detail elements on the models.

“I created a system of unconnected joints that act similar to cluster deformers but have the added advantage of easily paintable weight maps,” says Keller, who also used random key-frame generation scripts to add random movement to each joint. This gave the objects an organic jiggle-like motion.

“I could have used cloth or softbodies to do this as well, but the joint system was very fast and much easier to edit.”

The dynamic tools Keller used most often were Maya’s particle simulations and Hair, while to add atmosphere to environments he turned to particle sprites.

“I used volume emitters to fill the scene with particles, and then set the conserve of the particles to a low value, and layered numerous turbulence, drag, and vortex fields to achieve the look of material suspended in a thick liquid.”

The turbulence fields, reveals Keller, had a range of frequencies and intensities, and he allowed the particles to inherit the velocity of the fields. “In some cases I attached springs between the particles within a certain distance of each other, so the particles would react to fields more like a viscous goo.”

Some of the organisms were sub-division surface objects that were given a soft body motion via wrap deformers. Keller says: “To create the effect of goo I wrote a custom MEL script that scaled up the radius of blobby surfaces painted on geometry.”

This, he says, meant he could keyframe a custom control and fine tune the growth of the ‘blobbies’ across an object. In the very first shot Keller added some fine fur to a spore, which enhanced the lighting on the object and “added to its overall ickieness”, but in other instances he used animated displacement maps.

“I first rendered out a pass of paint- effects branches crawling across a surface,” Keller explains. “I then piped the rendered sequence into an animated displacement map, which gave the look of a crawling vein beneath the surface.

Lighting tricks

Without expertly applied lighting, of course, the sequence would not work, and to achieve this, Keller – like Yount at the outset of the project – turned to electron microscopy.

He says: “The look started with a version of the classic electron microscopy shader, where a ramp is plugged into the facing ration of the geometry so that parts of the surface that turn away from the camera glow and parts of the surface that face the camera are dark.

Although “this looked pretty good” Keller felt there was room for improvement, so he layered the shader with another ramp that caused shader glow that was based on surface luminance.

“I set up lights in the scene that just added pools of surface incandescence.” This, added with the electro-magnetic scanning look, created the look he was after – something more captivating than the typical microscopy look.

Keller rendered this out in Mental Ray with bump and displacement maps created in ZBrush. “I added an occlusion pass, luminance depth pass, a fog pass, motion blur vector pass, and some masking passes, and handed these off for compositing,” he explains.

The dynamic nature of the sequence posed a problem for Keller, because his original models were unsuited for extreme close-ups, so when he was given the final camera moves he re-engineered his shading strategy.

“The cameras were skimming extremely close to the surface of the models, and this required a number of layered procedural textures in the bump channel, as well as separating the models into high- and medium- resolution versions based on camera distance.

Also, displacement maps could not be used in the extreme close range because of resolution limitations. I exported my displacement maps from ZBrush at 2K and 4K, but even those were not high enough to hold up at the extreme close range.”

The solution? “I used those maps on parts of the model that were further away from the camera,” says Keller.

For the titles, Yount chose Linotype Normetica. “It is well designed and has a cold science-driven form.”

Almost every model for crafting the CG cellular environment started out in Pixologic's ZBrush 2.0.

The invasion journey started in space, entered the body, before ending up in a lab-type environment.

Follicle challenge

Maya Hair, meanwhile, was invaluable for crafting the pili on some of the ‘nasties’ that float around between the cells. “I also used Hair in several of the rigs for the tentacle that bursts through a surface in one of the shots,” says Keller. “An IK spline was attached to a dynamic hair-curve, which allowed for some interesting secondary motion.”

Texturing and rendering

Yount researched fine art photography to avoid the imagery looking like average CG cel animations. A book called Photomicrographs by Claudia Fahrenkemper gave inspiration. “I liked the crisp detail in the surfaces of the images, and that there were no specular highlights. For colour, I wanted it to be very dark and graphic, to give the feeling that we were inside the body.”